Automated analyzers are in common use today for assaying the contents of sample tubes for a variety of purposes. Conveyors are often included in these automated analyzers for transporting sample tubes to fluid transfer stations, where robotic pipettors, or other fluid transfer devices, transfer materials to or from the sample tubes. To ensure that materials are being accurately transferred by robotic pipettors, it is important that sample tubes being conveyed within an analyzer be maintained in substantially upright orientations. Additionally, for applications in which robotic pipettors are used to pierce penetrable closure devices associated with the sample tubes, it is also important that holders for carrying the sample tubes are also capable of retaining the sample tubes, as it is possible for the retaining forces of a closure device to exceed the withdrawal forces of a robotic pipettor, thereby resulting in the removal of a sample tube. Removal of a sample tube will interrupt the workflow of a laboratory and could result in the loss of a sample or, worse, contamination of an analyzer.